Teach me about MIG rectifiers

[NickJ]

A few weeks ago I was given a Cebora 175 mig, owner told me the rectifier was dead but still worked ok on low power, he won a fancy new MIG so it was just taking up space. Got around to checking it over today and found the wirefeed works and it makes sparks (no gas to check any further) I pulled the rectifier out to bench test but after a visual showed the diodes loosing their legs i'd say the initial observation is correct.

 

I'm told a new regulator is ~$200 but is there any reason I can't order diodes of ali and just replace whats there?

 

ie multiple of http://www.aliexpress.com/store/product/High-quality-ZP30A-2CZ-Spiral-rectifier-diodes-30A-200-2000V-Screw-the-rectifier-diode/2021064_32606157729.html

or http://www.aliexpress.com/item/MDS200A-3-Phase-Diode-Bridge-Rectifier-200A-Amp-1600V/537421812.html?spm=2114.01010208.3.54.UmBF3l&ws_ab_test=searchweb201556_10,searchweb201602_5_10037_10017_507_10032_401,searchweb201603_9&btsid=d1553b07-e0a7-44bb-89e7-1bdf81a6f70d

 

Plan is to rewire the output and run on flux core until I can sort a bottle and reg for CO₂

[chris r]

If the specs match up I'd say replace it. Its not like it cost you much or you can break it more than it already is 

[mike100]

You can use normal diodes and make a discrete bridge but check the current rating of the diodes carefully . The bus capacitors in the welder are normally what causes diodes to fail.once one fails then they will all go. Use standard recovery diodes about 70 amps and around1600 volts. That's because of the inrush current.

Use a good heat sink and make sure you remain within the ambient temperature range . They are the same type of diodes as used in automotive alternators

Good lucj

[mike100]

Inferior diodes often found in cheaper range of mig welders are prone to failure. Once one blows the rest will follow rapidly. Why? Because the type of diodes fitted in the bridge rectifier are linked together so that the sum of all of the diodes covers the amps and voltage generated by welding with the machine. These press fit diodes are the same as used in vehicle alternators.

Obviously installing these enables the welders to be sold at the lower end of the market and for a while they hold out but inevitably fail.

The diodes are installed in a heat sink made from aluminium. and install new Standard Recovery Vishay 70 amp 1600 volt diodes that collectively exceed the workload of these welders and provide a more robust machine with the ability to work at the lower end of the welding scale as well as the higher end with ease.